The present invention relates to a metal cutting bandsaw blade, and especially to an arrangement of teeth thereof. Bandsaws have long been used for cutting hard materials such as metal bars or profiles, their main advantage being that they can be made thinner than circular saws, thus wasting less material. Metal cutting bandsaw blades have some disadvantages that have restricted their use, however, since they tend to lose their torsional stiffness when the feed force is high. Many tooth shapes arrangements have been suggested with the purpose of reducing the feed force and any force components that might twist the blade. Well known among such tooth arrangements include having some teeth straight and longer than others to guide the tooth edge laterally, and letting teeth with unequal edge shapes cut thick but narrow chips known as the "triple chip" arrangement.
Lateral forces on the toothed edge of the bandsaw may be minimized if teeth that are subjected to large lateral forces are arranged in pairs with opposite setting. If the spacing between the teeth of the pair is small enough they will both be in the cut most of the time, and their individual lateral forces will cancel each other. However, if that spacing is small, then a larger number of teeth will be cutting simultaneously, leading to an undesirably large feed force when cutting solid sections, or a small depth of cut for each tooth, which is inefficient and produces excessive wear.
Another problem is the low in-plane stiffness for resisting feed forces acting in unison, with a great risk of vibration occurring if many teeth at equal spacing are cutting, causing chattering, noise and corrugations in the cut metal surfaces. On the other hand, if few teeth are cutting, the lateral forces will not cancel each other.
These problems make it difficult to design an optimal bandsaw even for a well defined metal cutting task, and even more so if the bandsaw is to be used for a variety of tasks involving metals of different thickness and metal types.
Numerous tooth arrangements have been suggested and tried in order to make a metal cutting bandsaw able to produce good surfaces in a variety of conditions. Differences in tooth height are used not only for lateral guidance, but also to let a few longer teeth do most of the cutting in hard materials still with a reasonable cutting depth. Differences in tooth spacing (pitch) are used to avoid chattering and to locate teeth in pairs without having too many teeth cutting at the same time. Differences in setting patterns are used to divide the kerf width into narrow chips with better thickness and controlled chip curling. But five or more teeth in the pattern may also occur, where lower (shorter) teeth have larger set widths than higher (taller) teeth.
For rational production, the teeth should be arranged in recurrent groups, corresponding to the widths of grinding, milling and setting tools. However, since it has been traditional to establish the setting of all teeth in the recurrent group simultaneously, very long recurrent groups require large tools, large machines and large machining forces.
Many suggested tooth arrangements, such as in Yoshida et al. U.S. Pat. No. 4,727,788 include all three of the above-discussed variations, i.e. variations in height, spacing (pitch), and setting, but are complicated and costly to manufacture.
It is an object of the invention to provide tooth arrangement for metal cutting bandsaw blades which causes less vibration than previously known designs, and which still is simple to manufacture with adequate precision.